Small Project Organization

Dependency Object

A small object can hold a dependency value and expose the operation that uses it.

dependency Instead of hiding a value in a global variable, store it in an object that receives it directly.
method A const method can use the stored value without changing the object.

Dependency Object

factor
dependency_object.cpp
Replay: real traced execution (multi-file project)
#include <iostream>

struct Multiplier {
    int factor;

    int apply(int value) const {
        return value * factor;
    }
};

int main() {
    int factor = 3;

    Multiplier multiplier{factor};
    int input = 7;
    int output = multiplier.apply(input);

    std::cout << "factor=" << factor << std::endl;
    std::cout << "input=" << input << std::endl;
    std::cout << "output=" << output << std::endl;
    return 0;
}

#include <iostream>

struct Multiplier {
    int factor;

    int apply(int value) const {
        return value * factor;
    }
};

int main() {
    int factor = 2;

    Multiplier multiplier{factor};
    int input = 7;
    int output = multiplier.apply(input);

    std::cout << "factor=" << factor << std::endl;
    std::cout << "input=" << input << std::endl;
    std::cout << "output=" << output << std::endl;
    return 0;
}

#include <iostream>

struct Multiplier {
    int factor;

    int apply(int value) const {
        return value * factor;
    }
};

int main() {
    int factor = 5;

    Multiplier multiplier{factor};
    int input = 7;
    int output = multiplier.apply(input);

    std::cout << "factor=" << factor << std::endl;
    std::cout << "input=" << input << std::endl;
    std::cout << "output=" << output << std::endl;
    return 0;
}

  1. factor ← 3, multiplier ← (empty), input ← 7

    11int main() {12    int factor→ 3 = 3; //@factor=2, 51314    Multiplier multiplier→ (empty){factor3};15    int input→ 7 = 7;16    int output = multiplier(empty).apply(input7);

  2. int apply(int value) const

    6int apply(int value7) const {7    return value7 * factor3;8}

  3. output ← 21

    15    int input = 7;16    int output→ 21 = multiplier(empty).apply(input7);1718    std::cout << "factor=" << factor3 << std::endl;19    std::cout << "input=" << input7 << std::endl;20    std::cout << "output=" << output21 << std::endl;21    return 0;22}
    outputfactor=3
input=7
output=21

  1. factor ← 2, multiplier ← (empty), input ← 7

    11int main() {12    int factor→ 2 = 2;1314    Multiplier multiplier→ (empty){factor2};15    int input→ 7 = 7;16    int output = multiplier(empty).apply(input7);

  2. int apply(int value) const

    6int apply(int value7) const {7    return value7 * factor2;8}

  3. output ← 14

    15    int input = 7;16    int output→ 14 = multiplier(empty).apply(input7);1718    std::cout << "factor=" << factor2 << std::endl;19    std::cout << "input=" << input7 << std::endl;20    std::cout << "output=" << output14 << std::endl;21    return 0;22}
    outputfactor=2
input=7
output=14

  1. factor ← 5, multiplier ← (empty), input ← 7

    11int main() {12    int factor→ 5 = 5;1314    Multiplier multiplier→ (empty){factor5};15    int input→ 7 = 7;16    int output = multiplier(empty).apply(input7);

  2. int apply(int value) const

    6int apply(int value7) const {7    return value7 * factor5;8}

  3. output ← 35

    15    int input = 7;16    int output→ 35 = multiplier(empty).apply(input7);1718    std::cout << "factor=" << factor5 << std::endl;19    std::cout << "input=" << input7 << std::endl;20    std::cout << "output=" << output35 << std::endl;21    return 0;22}
    outputfactor=5
input=7
output=35